The present invention relates to free fall vehicles for quick deployment to the ocean bottom; and more particularly to transponders or beacons operationally deployable from the surface of the ocean for embedment in an upright position on ocean bottoms having sediment of unknown consistency.
A quick and accurate beacon navigation system (BNS) has been developed for determining the geodetic position of a submarine or surface vessel. The system includes a free-fall vehicle which deploys a single acoustic beacon to the ocean floor, a hydrophone array mounted on the hull of the vessel for detecting acoustic signals from the beacon, and a signal processor for measuring the vessel's bearing angle relative to the beacon. The bearing measurements are combined with position and attitude obtained from other systems such as an inertial navigation system (INS) to yield accurate navigation data. Typically, the beacon is part of a buoy which is attached by means of a tether to an embedment anchor. Due to its size and lack of streamlining, the vehicle descends slowly and drifts with ocean current. For example, with an average ocean current of one-half knot, the vehicle may drift 3,000 feet in 20,000 feet of descent. The actual position of the deployed beacon after coming to rest must then be surveyed by time-consuming and costly procedures.
Streamlining the vehicle will increase the descent rate and ensure a more vertical trajectory, but the vehicle penetration depth in the sediment may be excessive, particularly where transponders and beacons must remain exposed above the sediment for optimum performance. The consistency (density, viscosity, firmness, etc.) of typical sediments, such as pelagic clay, calcareous ooze, and loose or medium sand, vary widely and is not usually known for the location of the vechicle deployment.